1. Field of the Invention
This invention relates to a liquid-filled anti-vibration device mainly used for supporting a vibration generator, e.g. an automotive engine.
2. Description of Related Art
As an engine mount or a liquid-sealed vibration-proof device for supporting and bearing an automotive engine or any other vibration generator so as not to transmit the vibrations to the vehicle body side, there is known the one that is provided with a partition bisecting the liquid chamber inside the vibration-proof device proper into a main liquid chamber and a subsidiary liquid chamber and being formed by an orifice, through which the main liquid chamber and the subsidiary liquid chamber communicate with each other so that a vibration damping function may be exhibited owing to the fluidization effect of the liquid via the orifice through both liquid chambers. Another ones are also known, wherein an elastic membrane or a movable plate is formed to the aforementioned partition.
The elastic membrane type and the movable plate type are equal in respect of the functionality (reduction effect of dynamic spring constant). With the elastic membrane type, however, since the rubber-like elastic membrane in a hemispherical form is vulcanization-bonded to the partition so as to block the opening of the partition, the rubber-like elastic membrane has limits in amplitude and in the event that an excessive external force is exerted on the rubber-like elastic membrane, a large hydraulic pressure is generated with the result that the elastic membrane is broken down or separated. Thus this was limited in reduction of the amplitude dependency.
On the other hand, the movable plate type is constructed so that stoppers limiting the movable area of the movable plate are provided at upper and lower parts of the partition and the movable plate is reciprocated within this movable area. Consequently, the movable plate impinges on the stoppers to generate an abnormal sound (hitting sound), and is subject to restriction in obviating the hitting sound.
In order to solve the above-mentioned problems, this invention is aimed at providing such a liquid-sealed anti-vibration device that despite adopting a shape difficult to generate the abnormal sound, the amplitude dependency can be reduced and the dynamic spring constant in a wide spectrum of median to high frequencies can be reduced.
The solution means for them resides in that a partition is provided to divide a liquid chamber formed between a vibration-isolating base and a diaphragm constituting an anti-vibration device proper into main liquid chamber and a subsidiary liquid chamber, and that the partition includes an orifice member having an orifice channel at a peripheral lateral part, a partition plate member crimped and fixed beneath the orifice member to the anti-vibration device proper thereby forcing an outer peripheral portion of an upper end of the orifice member to an outer peripheral end of the vibration-isolating base on the liquid chamber side, and a rubber-like elastic membrane disposed in a space formed between the orifice member and the partition plate member, the rubber-like elastic membrane having a base portion attached fixedly to the one of the orifice member and the partition plate member and an open terminal at its distal end, the open terminal being slidably brought into pressure contact with the other, thereby constituting a cantilevered sliding membrane structure.
According to the construction above, the rubber-like elastic membrane provided for the partition is, because of the cantilevered sliding membrane structure, free from interfering with the stopper under the normal oscillations, as is the case with the movable plate type, permitting the generation of the abnormal sound or hitting sound to be minimized. Furthermore, the open terminal of the rubber-like elastic membrane slides toward the other member differently from the prior art elastic membrane type that the opening of the partition is obstructed and hence, the amplitude dependency is minimized and the functions meeting required characteristics can be exhibited.
As a specific structure of the partition, such a constitution can be exemplified that the orifice member is configured in an annular form while the partition plate member is comprised of a cylindrical portion disposed inwards, a flange-like forcing portion extending from a lower end of the cylindrical portion radially outwardly to force the underside of the orifice member, and a crimped lock portion linking from the forcing portion at its radially outward side; and an annular space is formed between the cylindrical portion of the partition plate member and the annular inner peripheral wall of the orifice member and within this space the rubber-like elastic membrane is disposed.
In this case, it is possible to adopt either an embodiment wherein the base portion (an inner peripheral side) of the rubber-like elastic membrane is attached fixedly to the cylinder portion of the partition plate member and the open terminal (an outer peripheral end) at a distal end is in pressure contact with the annular inner peripheral wall of the orifice member so as to be freely slidable or another embodiment wherein the base portion (an outer peripheral side) of the rubber-like elastic membrane is attached fixedly to the annular inner peripheral wall of the orifice member and the open terminal (an inner peripheral end) is in slidably pressure contact with the side part of the cylindrical portion of the partition plate member.
As a fixedly attaching means for the base portion of the rubber-like elastic membrane, it is possible to adopt any embodiments, for example an embodiment of vulcanization bonding to the orifice member or the partition plate member, an embodiment of press-fitting in either of them, an embodiment of pinching and pressing between an inward projecting portion of the annular orifice member and the cylindrical portion of the partition plate member, or the like.
To restrain the sliding range of the rubber-like elastic membrane, it is desirable further to form a restraint portion for preventing the deformation of the rubber-like elastic membrane due to a large displacement at axially (orthogonal direction to the parting plane of the partition in the liquid chamber) both sides thereof. It will suffice that the restraint portion avails itself of both a protuberant portion projecting inwardly of a part of the annular inner peripheral wall and a part of the partition plate member. Also in this case, the rubber-like elastic membrane is of a cantilevered sliding membrane structure and consequently, it is possible to decrease sufficiently the generation of an abnormal sound as compared with the prior art movable plate type where the plate hits intermittently against the upper and lower stopper walls.
From the aspect of exhibiting a desired vibration damping function it is preferred that the open terminal of the rubber-like elastic membrane be made thick-walled because a contact area with the orifice member or the sliding wall of the partition plate member can be ensured and the leakage of liquid between the main liquid chamber and the subsidiary liquid chamber is obviated.
Further where the rubber-like elastic membrane is formed on its inner face with reinforcing ribs circumferentially at plural positions, it is possible to suppress any dimensional change of the rubber-like elastic membrane due to a hydraulic pressure difference between the main and the subsidiary liquid chambers, and this is suitable in maintaining the desired vibration-damping function.